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Jet Propulsion LaboratoryCalifornia Institute of Technology 1 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
The importance of being earnest about line shapes!!
Charles E. Miller and Linda R. Brown
Jet Propulsion Laboratory, California Institute of Technology
4800 Oak Grove Dr., Pasadena, California 91109
Acknowledgments
The research at the Jet Propulsion Laboratory (JPL), California Institute of Technology, was performed under contract with National Aeronautics and Space Administration.
Jet Propulsion LaboratoryCalifornia Institute of Technology 2 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
Return global XCO2 data with
0.3% precision
Our Research Goal: Improve CO2 and O2 line
parameters
Jet Propulsion LaboratoryCalifornia Institute of Technology 3 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
Better Accuracies Require Precise Knowledge/Control of the Experimental State
• Pristine cells – no contamination• Temperature monitoring inside the cell• Isotopic enriched samples• Mass spectrometric standard samples• Stable spectrometer performance
Goal for Experimental Uncertainties:Abundances: 0.05% (purity, Isotope)Pressure: 0.01 Torr (if P > 10 Torr)Temperature: 0.1 K Path: 2 mm (0.1%) Signal/noise: 2000:1 Resolution: nearly Doppler-limited100% Trans: 0.1% 0% Trans: 0.1%Instrumental line shape
FourTemp
Probes(PRT)goingInside
theCell
Jet Propulsion LaboratoryCalifornia Institute of Technology 4 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
Molecular Line Shape Problem!
Miller et al. Comptes Rendus Physique 6 (2005).
Voigt onlyStrange residuals Strange residuals (!)
Multispectrum retrievals one solution for all lines
fitting all spectra simultaneously
[modified from Benner et al. JQSRT 53, 705 (1995)]
NEW CO2 Lab parameters could not be used in (Voigt only) atmospheric retrievals.
non-Voigt line shapes (line mixing + speed
dependence + narrowing)
Jet Propulsion LaboratoryCalifornia Institute of Technology 5 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
Too many line shape choices!
Lisak et al. 2010 O2 B-band
Jet Propulsion LaboratoryCalifornia Institute of Technology 6 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
What we have to do now!
• Learn what combination of line shapes can produce the best atmospheric retrievals.
• Create and Validate universal software using the required molecular shapes to compute synthetic spectra (radiances etc….).
• Give standardized software to both atmospheric and lab spectroscopists:
So that new lab parameters will be consistent
with atmospheric calculations.
Jet Propulsion LaboratoryCalifornia Institute of Technology 7 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
Need to do better lab studies
• Use community-validated multi-spectrum retrieval codes that permit us to obtain consistent values of line shape parameters.
(do intercomparisons)• Use gas pressure that can
reveal all activated line shapes (Voigt, speed dependence, line mixing, narrowing …..).
• Excellent instrumental performance (usual stuff).
Conventional Strategy: Sequential L-B-L analyses
Quantum modeling Pres. (atm) 1st Positions: < 0.001 2nd Intensities: < ~ 0.010 To Create good database for broadening retrievals
3rd Shapes:Lorentz: 0.10 – 1. Narrowing & 0.03 – 0.1 Speed Dependence (Lorentz=Doppler)Line mixing: 0.5 – 10 Collision Induced Abs: 1 – 20 ?
Jet Propulsion LaboratoryCalifornia Institute of Technology 8 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
Constraining multispectrum fits!
• STRATEGY: Fit all lines and spectra simultaneously BUT• Constrain positions and intensities and adjust constants in the
quantum mechanical equations (instead of fitting line-by-line)• Pressure broadening parameters still fitted line-by-line
Line Positions:νi = ν0 + B(J(J+1)) - D(J(J+1))2 + H(J(J+1))3 – E" ν i Resonant frequency ν 0 Band origin J Rotational quantum number E" Lower state rotational energy
(fixed)
ν0, B, D, H, upper state constants of each band in the region, are the
adjusted instead of individual positions.
Line Intensities:Si = (i/0)(Sv/Li) exp(-hcEi″/kT)[1-exp(hcvi/kT)]F
Si, observed individual line intensity Sv vibrational band intensity,F Herman-Wallis factor = [1+A1m+A2m2+A3m3]2
Li Hönl-London factor, where li= (m2l″2)/|m| for CO2
m = J″+1 R branch, m = J″ for the P branchJ″, l lower-state rotational & angular momentum quanta Qr lower state rotational partition function at T0=296 KEi″ lower state rotational energy
Sv, A1, A2 are the adjusted parametersCan we do this for asymmetric tops? symmetric tops?
Jet Propulsion LaboratoryCalifornia Institute of Technology 9 V-1 11th HITRAN Conference, Cambridge, MA, June 16-18, 2010
CALL TO ACTION!
Fits to laboratory and atmospheric spectra must use the same line shape formulations
• Create new universal line shape (LS) software• Validate LS formulations• Expand databases to include all necessary LS parameters• Convince sponsors to fund it!
Coming goal: 0.1% accuracy for strongest bands